I've got a 5 gal tank with a couple goldfish in it at the office right now. Its boring. Everyone has seen goldfish before. What are some interesting things I can put in there that maybe you don't see in an aquarium? Thinking along the lines of plantlife, snails, shrimp, crab, etc...

Bought a setup with a small filtration system but outside of that everything must be pretty hardy, easy on the environment (so I don't overload the tank), low light, and fine at room temperature (maybe a little higher with the light turned on). If the suggestion is cool enough I am able to change the substrate and plantlife if needed.

Any suggestions would be appreciated. Thanks!